High resolution and fast chemical imaging using widefield optical photothermal infrared microscope

Abstract

Label-free infrared (IR) imaging reveals chemical bonds in specimens, but its limitations include a spatial resolution of approximately 5 µm. The advent of optical photothermal infrared (OPTIR) microscopy extends molecular fingerprint imaging by one order of magnitude near 500 nm. However, traditional scanning OPTIR faces a challenge of imaging speed. To improve speed and throughput, we employ pulsed visible probe light for widefield detection of transient photothermal responses induced by mid-infrared pulses. Our time-gated camera technique achieves sub-microsecond temporal resolution. We successfully imaged polystyrene beads, submicron SU8 polymer etchings, and mouse brain tissue samples using our widefield OPTIR microscope. The system excels in probe-dependent temporal and submicron spatial resolution, operating at 100 Hz over a 50 µm diameter field of view, while maintaining reasonable spectral fidelity. This enhanced widefield OPTIR microscopy promises rapid, label-free chemical imaging for biological samples and high-throughput screening applications.